Barge-in is the ability of an AI phone assistant to be interrupted by the caller mid-utterance — just like in a natural conversation. Without it, calls feel robotic because users have to wait for the system to finish speaking.
Technically it relies on continuous speech-to-text with voice-activity detection (VAD): the moment voice input is detected, the active TTS playback is cut and the system switches into listen mode. Thresholds and hysteresis matter — otherwise background noise hijacks the dialogue.
In production, barge-in improves perceived latency and conversion rates. Edge cases worth tuning: loud office noise, hold-music on the caller’s side, and very short confirmations ("yes", "okay") must be classified correctly to avoid ping-pong cuts.